Removal of selected pharmaceuticals and personal care products using greater duckweed constructed wetland followed by GAC sandwich slow sand filter

Removal of four emerging pharmaceuticals and personal care products (PPCPs) compounds from water (i.e. diethyltoluamide, paracetamol, caffeine and triclosan) were investigated and optimized using a novel Greater duckweed (Spirodela polyrhiza) based laboratory-scale free water constructed wetland (CW) followed by GAC (granular activated carbon) sandwich slow sand filtration (SSF) system. The extraction and detection methods were simplified and optimized without conditioning and equilibration for solid phase extraction (SPE), and without derivatization for gas chromatography-mass spectrometry (GC-MS). Effects of light intensity, aeration, E.coli abundance and plant biomass on the removal of target compounds at batch scale with the aid of experiment design were investigated. Continuous flow tests were conducted using optimized four factor levels, with and without post-treatment, using a stabilization tank (ST). The CW-ST system showed better performance than the CW alone and both showed good stability of removal after stopping aeration. However, poor removal of diethyltoluamide indicated the importance of further effluent treatment. Thus, GAC sandwich SSFs using coarse sand with different GAC layer depths at different filtration rates were further evaluated to remove target PPCP compounds. Filter of 10 cm sand/20 cm GAC/20 cm sand achieved the overall optimal average target PPCP removal (98.2 %) at 10 cm/h filtration rate. Both adsorption and biodegradation contributed to the removal during the filtration process. Type 1 pseudo-second-order model fitted best the adsorption kinetics of target PPCP compounds onto GAC and the adsorption isotherms were described by the Freundlich model. Finally, the optimized CW-ST and SSF systems were connected in series to verify removal of target PPCPs from both synthetic wastewater and natural water. Average removal of above 95 % was achieved for all compounds in the combined system and the system performance presented good stability, suggesting application of the CW-SSF system for removal of PPCPs from water.